The present invention relates to a transparent electroconductive film having a polymer film and a transparent electroconductive layer deposited on the polymer film, wherein the electroconductive layer is resistant fully to delamination or removal and the electroconductive film has good electrical characteristics and good durability. The present invention also relates to a touch panel provided with the transparent electroconductive film.
A resistive touch panel is widely used as an input unit for a household appliance or a portable terminal because the touch panel is easy to be miniaturized, lightened, and thinned. When a user pushes a part of the touch panel or draws with a specialized pen on a part of the touch panel, the part comes into contact with an opposing electrode, so that the portion and the electrode are electrically connected and a signal is inputted.
As shown in FIG. 4, a typical resistive touch panel has a lower electrode 3 having a glass plate 1 and a transparent electroconductive layer 2 deposited thereon; an upper electrode 6 having a polymer film 4 and a transparent electroconductive layer 5 deposited thereon; and spacers (microdot spacers) 7 interposed between the transparent electroconductive layers 2 and 5. Pressing the display surface of the upper electrode 6 with a finger or a pen makes the upper electrode 6 and the lower electrode 3 into contact with each other, so that these electrodes are electrically connected and a signal is inputted. The surface of the upper electrode 6 is overlaid with a hard-coating layer 8 for protecting the polymer film 4. Since the surface of the upper electrode 6 is rubbed with a finger or pen, the upper electrode requires resistance to wear, and therefore is provided with the hard-coating layer 8.
Japanese Patent H2-194943A discloses that after ITO (indium tin oxide) transparent electroconductive layer is deposited, heat treatment is conducted so as to crystallize ITO, for improving durability of the transparent electroconductive film for touch panel. However, since the substrate of the transparent electroconductive film is a polymer film, the temperature for the heat treatment is limited. The heat treatment thus needs to be conducted at relatively low temperature and for a long time, such as at 150xc2x0 C. and for 24 hours. This causes problems of low productivity and high production cost.
In such a touch panel, with the input with a finger or pen, the transparent electroconductive layer 5 of the upper electrode 6 and the transparent electroconductive layer 2 of the lower electrode 3 are contacted and uncontacted repeatedly. The transparent electroconductive material such as ITO, which is a material for depositing transparent electroconductive layers 2, 5, has low resistance to wear and indentation. Therefore, in the transparent electroconductive layer 2 or 5, the transparent electroconductive layer 5 of the upper electrode 6, which deforms repeatedly during the input to the touch panel, is particularly easy to be cracked. In addition, the transparent electroconductive layer 5 is easy to be delaminated and removed from the polymer film 4 due to the repeated contact and uncontact of the transparent electroconductive layers 2 and 5, which are made of the same material.
When the transparent electroconductive layer 5 of the upper electrode 6 is damaged or delaminated, electrical resistivity of the surface of the transparent electroconductive layer 5 changes, and uniformity of the electrical resistivity is lost, thereby spoiling electrical properties, and thus the precise input can not be carried out. These cause a decrease in reliability of the touch panel, damages, defects, and a decrease in durability.
It is an object of the present invention to solve the aforementioned conventional problems, to provide a transparent conductive film comprising a polymer film and a transparent conductive layer deposited on the polymer film, which can realize a touch panel having no problem of damage and delamination of the transparent conductive layer, and having good reliability and durability, and to provide a touch panel provided with the transparent conductive film.
A transparent conductive film of the present invention has a polymer film, a transparent conductive layer deposited on the polymer film, and moreover, a protective layer, preferably made of material different from the transparent conductive layer, formed on the transparent conductive layer.
The surface of the transparent electroconductive layer is covered with the protective layer, so that physical or chemical stresses generated during the input to the touch panel do not affect transparent electroconductive layer directly, thus preventing damages and delamination of the transparent electroconductive layer.
Furthermore, the protective layer formed on the transparent electroconductive layer improves the strength of the transparent electroconductive film, thereby enhancing a resistance to wear.
In the present invention, though the protective layer is provided for improving durability of the transparent electroconductive layer, the improvement in a total luminous transmittance of the transparent electroconductive film and the control of its color shade also can be carried out by designing the refractive index, the thickness and the structure of lamination of the protective layer suitably. As a result, properties and functional characteristics of the transparent electroconductive film can be more improved.
The material constituting the protective layer applied in the present invention is not particularly limited and can be chosen from those that can provide an improved strength and an enhanced resistance to wear to the transparent electroconductive film. The material may be the same as or different from that of the transparent electroconducitve film. The protective layer of the present invention comprises preferably at least one selected from the group consisting of oxides, nitrides, carbides, carbon, and composites of these compounds (for example, oxidized nitride) as the main component, more preferably, at least one selected from the group consisting of C, CNx, BNx, BxC and SiCx as the main component. Or the protective layer may be a transparent thin film comprising oxide, nitride or oxidized nitride of at least one material selected from the group consisting of Si, Ti, Sn, Nb, In, Mg, Ta and Zn, more concretely, at least one selected from the group consisting of SiOx, TiOx, SnOx, NbOx, InOx, MgFx, TaOx and ZnOx.
The thickness of the protective layer is preferably from 0.5 nm to 100 nm.
The protective layer is preferably a thin film formed by a physical depositing method such as vacuum evaporation method, sputtering method, ion plating method, and laser ablation method, or by a chemical depositing method such as CVD method, particularly a thin film made of SiCx, SiCxOy, SiCxNz, or SiCxOyNz formed by sputtering method by using a SiC target. In this case, the SiC target preferably has a density of 2.9 g/cm3 or more. Particularly, it is desirable that the SiC target obtained by sintering a mixture of silicon carbide powder and nonmetal-based sintering assistant is used.
The protective layer of the present invention may be formed by coating the transparent electroconductive layer with a material therefor as it is or with a liquid substance including the material therefor and a solvent such as alcohol, ketone, toluene, hexane, etc.
The transparent electroconductive film of the present invention preferably has a surface resistivity of 300 to 2000 xcexa9/Sq. at a side where the protective layer is formed and a linearity value of not greater than 1.5%.
The linearity value is an index for indicating uniformity of the resistivity of a transparent electroconductive film. The linearity value can be expressed as follows.
Electrodes made of Ag paste or the like are provided at two sides of the transparent electroconductive film which are opposite to each other, and a direct voltage is applied to the two electrodes. It is defined that L is a distance between the two electrodes and V is an applied voltage. Then, at arbitrary points on the transparent electroconductive film, distances 1 from the points to the negative electrode and potential differences v from the points to the negative electrode are measured, respectively.
The linearity value is expressed as the following formula.
Linearity (%)=|1/Lxe2x88x92v/V|xc3x97100 
The smaller the linearity value, the better the uniformity of the resistivity. When the linearity value is 0%, the resistivity is perfectly uniform. In case of a resistive touch panel, a linearity value is preferably not greater than 1.5%.
The transparent electroconductive layer of the present invention is preferable to be made of a transparent conductive oxide (TCO) of indium oxide system (including a system doped with indium oxide), a TCO of indium oxide and tin oxide (ITO), or a TCO of indium oxide and zinc oxide (IZO).
The touch panel of the present invention is provided with such a transparent electroconductive film of the present invention.